Hello,

I'm working on a project where I'm making a combination light sensor + motion sensor that will be attached to a 12V LED strip. The idea is that during the day the strip would stay off, and at night the strip would only turn on when the PIR detects motion, then turn off after some time. I've found some sample circuits and recreated a design here, but I can't get the PIR portion to properly trigger. I suspect that I'm laying this out on my breadboard wrong somehow, but I'm starting to think there's something with the PIR sensor that I'm not accounting for. Can someone take a look at my planned circuit and see where I'm going wrong? The PIR i'm trying to use is the ZRE200GE (https://www.zilog.com/docs/zmotion/PS0402.pdf).

 

Hi edge,
Do you have a Fresnel lens over the photo detector?
E
https://www.willow.co.uk/vmchk/Infrared-PIR-Fresnel-Lenses/View-all-products.html

 

Hi Eric,

Yes, I've tried both with and without a small Fresnel lens. The lens that I currently have access too is the small variety meant to snugly fit around the PIR itself, not the larger variety.

 

hi,
What voltages do you measure on D & G.
Make sure you have Photo sensor pin out correct.

Post a photo if possible
E

The 555 Trig pin #2 is normally high, pulled low to trigger

 

Reading under 1v across D and G on the PIR when the lights are on. When off it’s going up to over 10v

attached some photos of the setup so far. Only thing I’ve intentionally left out is the last 100 ohm resistor cause I wanted the light strip brighter.

 

Hi @edge231
This is your circuit in LTSpice simulation, it works OK.
Two images, Dark and Light on LDR.
Shortened 555 ON time for the simulation.
Will look over your photo shots.
E

 

Reading under 1v across D and G on the PIR when the lights are on. When off it’s going up to over 10v
attached some photos of the setup so far. Only thing I’ve intentionally left out is the last 100 ohm resistor cause I wanted the light strip brighter.

Hi,
Reading under 1v across D and G on the PIR when the lights are on
I guess you mean the Day/Night test of the LDR section?

Only thing I’ve intentionally left out is the last 100 ohm resistor cause I wanted the light strip brighter.
Post a circuit showing the light strip etc..

Note that some PIR's can be a little temperamental when first powered up, need a few seconds to stabilize.

E
There is a difference in the load of the Source of the example circuit and yours?

 

Thanks for taking a look at this for me. I noticed that in your simulation circuit you've got the PIR D connected after R4, and in mine I have it connected before. Do I have that part wrong or am I overlooking something?

When I tested the voltage across D and G, yeah that was testing it while flipping ambient light in room off and on.

The light strip is connected after the 100 ohm resistor at the end of my circuit. Where I have the +12V at the end is exactly where I'm placing it. V+ from the strip connecting there, and V- going to ground. You can see a portion of the strip lit up in one of my pictures (should be the first one). May end up making the 1k resistor after the 555 output smaller to make it even brighter but not sure if I need that yet.

As for that missing resistor, I can try to add that in to see if that makes any difference. Since I have the transistor in that area, would I be placing that before pin 2 or after pin 3 of the 2N3904? Thinking after pin 3 but not sure.

 

Hi,
That simulation voltage source V1 is to generate a positive going pulse/s to drive Q2 Base.

My concern about your circuit compared to the original datasheet, is when the PIR detects movement the
S pin is shorted to 0V via the transistors Base to Emitter junction.

The original document shows a 47k from S to 0v.

E

 

Just tried adding a few different sizes of resistors around Q2 in a couple different positions. Didn't seem to help any. Light strip wouldn't even light up when I messed with that part.

I decided to start fresh and after pulling my jumpers and starting my breadboard over, only thing that seems to be working now is the LDR part. Strip comes on and stays on when the ambient light is off, but now it's not turning back off, and PIR still not triggering anything.

 

hi edge,
Build and test just this part of the circuit, lets know the result.
E

Added a sim of that circuit.

 

Getting mixed results with that test circuit with just the PIR. Sometimes the PIR will trigger the light, sometimes it won't. Tried swapping out the transistor to see if i had a faulty one on my breadboard but it seemed to make things worse. Also tried swapping the PIR out for a different one (same model) and still same results.

Only thing that seems to work reliably is physically touching the R5 1k resistor on both sides to force the trigger. PIR doesn't seem to want to do it on its own. Starting to think i need to work with a different PIR.

 

hi edge,
I am starting to believe that datasheet is misleading?
They are using a 72db amplifier.
This is another datasheet, it includes your model.
E

 

http://www.glolab.com/pirparts/pirmanual.PDF

I’ve always used these circuits when deploying a PIR

 

Hi edge,
I use this PIR module on my security system, +3V out when triggered, works from 5V through 20v,
Adjustable sensitivity and On period, eBay.
E

 

If I didn't have size limitations on where I'm installing the PIR I would totally just get a prebuilt module and use that. Right now what I'm trying to do is get this circuit working so that I can install it into a custom pcb that will be approx 10-12mm wide, under 90mm long, and keep within a depth of about 8mm or less. Trying to fit this into an aluminum channel for an LED strip.

With the new spec sheet you find, I'm noticing that it also says max operating voltage of 10v. Wonder if my constant playing with it at 12v did any damage to it. Going to try a fresh one and keep my voltage under 10 to see if I get better results.

In the mean time, do you know of any other PIR sensors that I could use in my circuit that doesn't rely on a prebuilt module? Been banging my head at this problem for a while and thinking a new PIR may be necessary.

 

Getting mixed results with that test circuit with just the PIR

In Eric's post #11 circuit, try increasing R4 to 50kΩ.

If that doesn't work, try adding an extra PNP transistor at the input to increase the 555 trigger sensitivity (below):

 

Increased R4 to 47k (closest resistor I had to 50k), didn't work. All that seemed to do is keep the light strip on instead of it turning itself off eventually. Was able to get it to turn back off when I tried a 22k but the PIR still wasn't triggering anything.

Also tried the extra transistor setup, no change. I'm either missing something major in my breadboard skills, or I'm just bad with these PIR's.

 

Have you measured the output voltage from the PIR?

 

Last time I measured it was about 0.3V coming out of pin 2 from the PIR.

So looking into it more it does sound like I do need a pull down resistor going from source to ground on the PIR, but adding that into my circuit didn't seem to help much. I'm guessing I need to keep playing with the size of that resistor to get results cause their datasheet mentions a 47k res @ 5v and looking at other info online related to this subject seems to indicate as such.